Method and an arrangement in a first network node for managing congestion

ABSTRACT

A method and an arrangement ( 400 ) for managing congestion of outgoing data of at least one link in a telecommunications signalling network protocol stack, comprising a first and second layer and an interface there-between, are provided. The first network node comprises multiple processing modules ( 430 ). The first network node ( 110 ) determines ( 210 ) a congestion level between the first and second layers. The first network node ( 110 ) receives ( 220 ), from the first layer, any existing first layer congestion level indication, indicating congestion between the first layer of the first network node and the first layer of the second network node. The first network node ( 110 ) generates ( 230 ) a simulated first layer congestion level indication based on the determined congestion level. The first network node ( 110 ) generates ( 240 ) a total first layer congestion level indication based on the simulated first layer congestion level indication and said any existing first layer congestion level indication.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 35 U.S.C. §371 National Phase Entry Applicationfrom PCT/EP2010/054838, filed Apr. 13, 2010, and designating the UnitedStates, the disclosure of which is incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a method and an arrangement in a firstnetwork node for managing congestion of outgoing data of at least onelink in a telecommunications signalling network protocol stack.

BACKGROUND

In a SS7 and/or SIGTRAN system, congestion and Send Failure Notificationhave been implemented. Congestion or send failure appears when the peerdo not acknowledge messages fast enough compared to the traffic rate inthe interface between the peer node and the layer 2 instance on thelocal node. This means that in case the traffic rate is too highcompared to the throughput of the interface between peer's layer 2instances, a congestion indication or a send failure notification willbe sent by the local layer 2 instance to the local layer 3 instance toindicate that there is an congestion situation, or overload situation.This indication is then forwarded to the client on top of layer 3 orforwarded to other nodes in case the local node acts as a gateway.

The mechanism to detect an overload situation in the interface betweenlayer 2 and layer 3 for the incoming direction is known from the abovementioned systems.

Layer 3, for example M3UA, buffers data when it receives a Send FailureNotification (SFN) in existing implementations of SS7 network protocolstacks.

Presently, flow control for outgoing SS7 traffic is handled by the useof process priorities. The clients have had lower priority, therebymaking it impossible to load the interface between layer 2 and layer 3higher than the processing unit can manage.

As a result of the introduction of multi core processors in CPP(Connectivity Packet Platform), present solutions for flow control needto be improved. The process priorities are effectively disabled by themulti core environment. Due to this there is a need to implement a flowcontrol function to make sure that the system is not overloaded bymessages. The overload can cause various problems like lost data orcrashing processes.

SUMMARY

An object of the present invention is to manage congestion (or overload)of outgoing data of at least one link in a telecommunications signallingnetwork protocol stack, wherein the telecommunications signallingnetwork protocol stack is implemented in a network node comprisingmultiple processing modules.

According to an aspect of the invention, the object is achieved by amethod in a first network node for managing congestion of outgoing dataof at least one link in a telecommunications signalling network protocolstack, comprising a first and a second layer and an interfacetherebetween. Each said at least one link interconnects the firstnetwork node and a second network node. The first network node comprisesmultiple processing modules. A communication network comprises the firstand second network nodes. First layer congestion level indication isbased on congestion between the first layer of the first network nodeand the first layer of the second network node. In a step, the networknode determines a congestion level between the first and second layers.In another step, the network node receives, from the first layer, anyexisting first layer congestion level indication, indicating congestionbetween the first layer of the first network node and the first layer ofthe second network node. In a further step, the network node generates asimulated first layer congestion level indication based on thedetermined congestion level between the first and second layers. In yetanother step, the network node generates a total first layer congestionlevel indication based on the simulated first layer congestion levelindication and said any existing first layer congestion levelindication.

According to a further aspect of the invention, the object is achievedby an arrangement in a first network node for managing congestion ofoutgoing data of at least one link in a telecommunications signallingnetwork protocol stack, comprising a first and a second layer and aninterface therebetween. Each said at least one link interconnects thefirst network node and a second network node. The first network nodecomprises multiple processing modules. A communication network comprisesthe first and second network nodes. First layer congestion levelindication is based on congestion between the first layer of the firstnetwork node and the first layer of the second network node. Further, atleast one of said multiple processing modules is configured to determinea congestion level between the first and second layers. The arrangementfurther comprises a receiving unit configured to receive, from the firstlayer, any existing first layer congestion level indication, indicatingcongestion between the first layer of the first network node and thefirst layer of the second network node. Moreover, said at least one ofsaid multiple processing modules is configured to generate a simulatedfirst layer congestion level indication based on the determinedcongestion level between the first and the second layer, and to generatea total first layer congestion level indication based on the simulatedfirst layer congestion level indication and said any existing firstlayer congestion level indication.

An idea of the present invention is to generate the total first layercongestion level indication based on the simulated first layercongestion level indication and said any existing first layer congestionlevel indication. Then, the generated total first layer congestion levelindication is sent from the interface to the second layer. As a result,the above mentioned object is achieved.

Advantageously, flow of outgoing data can be controlled without anymodification to the first and second layers. In this manner,implementation at a low cost is facilitated.

It is to be understood that the expression “multiple processingmodules”, includes, but is not limited to, a plurality of processingunits, such as CPUs or the like, or one single processing unitcomprising a plurality of processing cores, commonly referred to as amulti-core processor.

Further features of, and advantages with, the present invention willbecome apparent when studying the appended claims and the followingdescription. It is to be understood that different features of thepresent invention may be combined to create embodiments other than thosedescribed in the following, without departing from the scope of thepresent invention, as defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects of the invention, including its particular featuresand advantages, will be readily understood from the following detaileddescription and the accompanying drawings, in which:

FIG. 1 shows a schematic overview of a communication network, to whichthe present invention may be applied,

FIG. 2 shows a schematic, combined signalling and flow chart of anexemplifying embodiment of the method in the first network nodeaccording to the present invention,

FIG. 3 shows a schematic block diagram of exemplifying layers andinterfaces of the first and second network nodes,

FIG. 4 shows a schematic flow chart of an embodiment of the method inthe first network node,

FIG. 5 shows a schematic block diagram of an embodiment of thearrangement in the first network node,

FIG. 6 shows a schematic, exemplifying combined signalling and flowchart of an embodiment of the method in the first network node, and

FIG. 7 shows a schematic, exemplifying combined signalling and flowchart of another embodiment of the method in the first network node.

DETAILED DESCRIPTION

Throughout the following description similar reference numerals havebeen used to denote similar elements, parts, items or features, whenapplicable.

FIG. 1 shows a schematic overview of a communication network 100, towhich the present invention may be applied. The communication network100 comprises a first network node 110 and a second network node 120.The first network node 110 may, for example, be a Media Gateway (MGW), aradio network controller (RNC), base station controller (BSC) and thelike. Likewise, the second network node 110 may, for example, be a MediaGateway (MGW), a radio network controller (RNC), base station controller(BSC), a Serving GPRS Support Node (SGSN) and the like. An arrow A1indicates that at least one link (or sometimes referred to asassociation) interconnects the first network node 110 and the secondnetwork node 120. The direction of the arrow indicates that said atleast one link is associated with at least outgoing data (or outgoingtraffic) in respect of the first network node 110. Possibly, said atleast one link is also associated with incoming data (or incomingtraffic) in respect of the first network node 110.

With reference to FIG. 2, there is shown a schematic, combinedsignalling and flow chart of an exemplifying embodiment of the method inthe first network node according to the present invention. The followingsteps may be performed in the first network node 110. Notably, the orderof the steps may differ from what is shown below for other embodimentsof the method in the first network node.

-   210 The network node 110 determines 210 a congestion level between    the first and second layers based on, for example, the number of    outstanding messages.-   220 The first layer sends 220, to the network node 110, any existing    first layer congestion level indication, indicating congestion    between the first layer of the first network node and the first    layer of the second network node. Any existing first layer    congestion level indication shall be understood to indicate whether    there is any first layer congestion level indication. Such first    layer congestion level indication is received from the first layer    as an indication that there is congestion on said at least one link    between the first layer of the first network node 110 and the first    layer of the second network node 120. Then this will be taken into    account, when generating the total first layer congestion level    indication in step 240 below.-   230 The network node 110 generates 230 a simulated first layer    congestion level indication based on the determined congestion level    between the first and second layers.-   240 The network node 110 generates 240 a total first layer    congestion level indication based on the simulated first layer    congestion level indication and said any existing first layer    congestion level indication. Expressed differently, the network node    110 generates 240 a total first layer congestion level indication    based on the simulated first layer congestion level indication and    any first layer congestion level indication if such has been    received in the step 220. In this manner, sequence problems in case    of congestion in both the interface between the first layers in the    first and second network nodes, respectively and the interface    between the first and second layers may be avoided.-   250 Optionally, the network node 110 aggregates 250 the simulated    first layer congestion level indication and said any existing first    layer congestion level indication to form the total first layer    congestion level indication.-   260 Optionally, the second layer receives 260 from the interface the    total first layer congestion level indication, if the steps above    are performed in the interface.-   270 Optionally, if the steps above are performed in the second    layer, the second layer makes the total first layer congestion level    indication available.

As a result, the second layer may be aware of overload situation, notonly between first layers in the first and second network nodes 110,120, respectively, but also about overload in the interaction betweenthe first and second layers.

FIG. 3 shows a schematic block diagram of exemplifying layers andinterfaces of the first and second network nodes 110, 120. The firstnetwork node 110 comprises, in the telecommunications signalling networkprotocol stack implemented therein, a first layer L1-1, an interfaceL3-1 and a second layer L2-1. Communication between the first layer L1-1of the first network node 110 and the second layer L2-1 of the firstnetwork node 110 is handled via the interface L3-1 of the first networknode 110. Similarly, the second network node 120 comprises, in thetelecommunications signalling network protocol stack implementedtherein, a first layer L1-2, an interface L3-2 and a second layer L2-2.Communication between the first layer L1-2 of the second network node120 and the second layer L2-2 of the second network node 120 is handledvia the interface L3-2 of the second network node 120. Data leaving thefirst network node is passed from the second layer L2-1 to the firstlayer L1-1 via the interface L3-1. The data is then passed to the firstlayer L1-2 of the second network node 120 for further progressing to thesecond layer L2-2 of the second network node 120 via the interface L3-2of the second network node 120.

In FIG. 4, there is shown a schematic flow chart of an embodiment of themethod in the first network node 110 for managing congestion of outgoingdata of at least one link in a telecommunications signalling networkprotocol stack, comprising a first and a second layer and an interfacetherebetween. Each said at least one link interconnects the firstnetwork node 110 and a second network node 120. The first network node110 comprises multiple processing modules. A communication network 100comprises the first and second network nodes 110, 120. First layercongestion level indication is based on congestion between the firstlayer of the first network node 110 and the first layer of the secondnetwork node 120. The following steps may be performed. Notably, theorder of the steps may differ from what is shown below for someembodiments of the method.

-   210 The network node 110 determines 210 a congestion level between    the first and second layers.-   220 The network node 110 receives 220, from the first layer, any    existing first layer congestion level indication, indicating    congestion between the first layer of the first network node and the    first layer of the second network node.-   230 The network node 110 generates 230 a simulated first layer    congestion level indication based on the congestion level.-   240 The network node 110 generates 240 a total first layer    congestion level indication based on the simulated first layer    congestion level indication and said any existing first layer    congestion level indication.-   250 Optionally, the network node 110 aggregates 250 the simulated    first layer congestion level indication and said any existing first    layer congestion level indication to form the total first layer    congestion level indication.-   260 Optionally, if the steps above are performed in the interface,    the interface sends 260 to the second layer the total first layer    congestion level indication.-   270 Optionally, if the steps above are performed in the second    layer, the second layer makes the total first layer congestion level    indication available.

In some embodiments of the method in the first network node 110, themethod is performed in the interface. Preferably, the method furthercomprises a step of sending 260 to the second layer the total firstlayer congestion level indication.

In some embodiments of the method in the first network node 110, themethod is performed in the second layer. Preferably, the method furthercomprises a step of making 270 the total first layer congestion levelindication available to the second layer.

In embodiments of the method in the first network node 110, a higherlayer comprises the interface and the second layer.

In some embodiments of the method in the first network node 110, thetotal first layer congestion level indication comprises the simulatedfirst layer congestion level indication, if the simulated first layercongestion level indication indicates worse congestion than said anyexisting first layer congestion level indication, or said any existingfirst layer congestion level indication, if said any existing firstlayer congestion level indication indicates worse congestion than thesimulated first layer congestion level indication. For example, thetotal first lay congestion level indication comprises the one of thesimulated first layer congestion level indication and said any existingfirst layer congestion level indication that indicates the highest levelof congestion. It is to be understood that the highest level ofcongestion indicates which of the simulated first layer congestion levelindication and said any existing first layer congestion level indicationis the most congested (or overloaded).

In some embodiments of the method in the first network node 110, thetelecommunication signalling network protocol stack comprises an SS7network protocol stack.

In some embodiments of the method in the first network node 110, thefirst layer comprises layer-2 of the SS7 network protocol stack,preferably layer-2 is one of MTP2, NNI-SAAL or SCTP.

In some embodiments of the method in the first network node 110, thesecond layer comprises layer-3 of the SS7 network protocol stack.

In some embodiments of the method in the first network node 110, thelayer-3 is MTP3, when layer-2 is MTP2 or NNI-SAAL, or the layer-3 isM3UA, when layer-2 is SCTP.

In some embodiments of the method in the first network node 110, saidfirst layer congestion indication comprises layer-2 congestionindication, when the second layer is MTP3 or MTP3b, or Send FailureNotification, when the second layer is M3UA.

In FIG. 5, there is shown an exemplifying embodiment of an arrangement400 in a first network node 110 for managing congestion of outgoing dataof at least one link in a telecommunications signalling network protocolstack, comprising a first and a second layer and an interfacetherebetween. Each said at least one link interconnects the firstnetwork node 110 and a second network node 120. The first network node110 comprises multiple processing modules 430. A communication network100 comprises the first and second network nodes 110, 120. First layercongestion level indication is based on congestion between the firstlayer of the first network node 110 and the first layer of the secondnetwork node 120. Further, at least one of said multiple processingmodules 430 is configured to determine a congestion level between thefirst and second layers. The arrangement 400 further comprises areceiving unit 420 configured to receive, from the first layer, anyexisting first layer congestion level indication, indicating congestionbetween the first layer of the first network node 110 and the firstlayer of the second network node 120. Moreover, said at least one ofsaid multiple processing modules 430 is configured to generate asimulated first layer congestion level indication based on thecongestion level between the first layer and second layers, and togenerate a total first layer congestion level indication based on thesimulated first layer congestion level indication and said any existingfirst layer congestion level indication.

In some embodiments of the arrangement 400 in the first network node110, the arrangement 400 further comprises a sending unit 410 configuredto send to the second layer the total first layer congestion levelindication, if the interface is configured to perform the steps above.

In some embodiments of the arrangement 400 in the first network node110, the second layer may be configured to perform the steps above.Preferably, said at least one of said multiple processing modules 430 isconfigured to make the total first layer congestion level indicationavailable to the second layer.

In some embodiments of the arrangement 400 in the first network node110, said at least one of said multiple processing modules 430 isconfigured to aggregate the simulated first layer congestion levelindication and said any existing first layer congestion level indicationto form the total first layer congestion level indication.

In some embodiments of the arrangement 400 in the first network node110, the total first layer congestion level indication comprises thesimulated first layer congestion level indication, if the simulatedfirst layer congestion level indication indicates worse congestion thansaid any existing first layer congestion level indication, or said anyexisting first layer congestion level indication, if said any existingfirst layer congestion level indication indicates worse congestion thanthe simulated first layer congestion level indication. For example, thetotal first lay congestion level indication comprises the one of thesimulated first layer congestion level indication and said any existingfirst layer congestion level indication that indicates the highest levelof congestion. It is to be understood that the highest level ofcongestion indicates which of the simulated first layer congestion levelindication and said any existing first layer congestion level indicationis the most congested (or overloaded).

In some embodiments of the arrangement 400 in the first network node110, the telecommunication signalling network protocol stack comprisesan SS7 implementation.

In some embodiments of the arrangement 400 in the first network node110, the first layer comprises layer-2, preferably layer-2 is one ofMTP2, NNI-SAAL or SCTP.

In some embodiments of the arrangement 400 in the first network node110, the second layer comprises layer-3.

In some embodiments of the arrangement 400 in the first network node110, the layer-3 is MTP3, when layer-2 is MTP2 or NNI-SAAL, or thelayer-3 is M3UA, when layer-2 is SCTP.

In some embodiments of the arrangement 400 in the first network node110, said first layer congestion indication comprises layer-2 congestionindication, when the second layer is MTP3 or MTP3b, or Send FailureNotification, when the second layer is M3UA.

FIG. 6 shows a first exemplifying, schematic combined signalling andflow chart of an embodiment of the method in the first network node 110for managing congestion of at least one link in a SS7 network protocolstack, comprising a layer-2, denoted L1-1, and a layer-3, denoted L2-1,and an interface, denoted L3-1, therebetween. The first network node 110comprises multiple processing modules. The layer-2 is MTP2 or NNI-SAAL.The layer-3 is MTP3. Said at least one link interconnects the firstnetwork node 110 with a second network node 120. Flow control for allinternal interfaces, per each said at least one link independently, maybe based on a congestion mechanism. The principle of the congestionmechanism is that separate flow control for each said at least one linkis provided in order to regulate (or control) outgoing data by means ofcongestion indications only for those links that carry high amount ofdata. At the same time, it is desired to avoid raising congestionindications for other links of the particular overloaded layer-2instance, i.e. overload between layer-2-layer-2. Some links may notcarry data at all at the moment of layer-2 instance overload, so it isinappropriate to mark them as congested. The principle is the same forall types of links, such as MTP2 NB, MTP2 HSL and NNI-SAAL. Three levelsof congestions are introduced to handle overload, where zero (0)indicates no congestion and 1-3 indicate three different levels ofcongestion. N denotes the congestion level for congestion betweenlayer-2 in the first network node and layer-2 in the second network node(see FIG. 3) for each said at least one link. K denotes the congestionlevel for congestion between layer-2 and layer-3 in the first networknode, also referred to as internal congestion, for each said at leastone link. N and K may hence assume any of the values 0, 1, 2 or 3. Thedotted lines may indicate the steps introduced in this example. Thefollowing steps may be performed. Notably, the order of the steps maydiffer from what is shown below for some embodiments of the method.

-   610 The interface L3-1 receives 610 congestion level N from the    layer-2. The interface may receive such congestion level N at any    time.-   620 The interface L3-1 sends 620 the maximum congestion level of N    and K.-   630, 640 The interface L3-1 passes 630, 640 data from the layer-3    L2-1 to the layer-2 L1-1 640.-   650 The interface L3-1 increments 650 the counter K with 1 if the    numbers of non-acknowledged messages are above a certain threshold.    In this manner, internal congestion is simulated. Advantageously,    the layer-3 L2-1 may be aware of overload situation, not only    between layer-2 instances in the first and second network nodes 110,    120, respectively, but also of overload situation in the interaction    between the layer-2 and the layer-3 (referred to as internal    congestion) as indicated by the counter K.-   660 The interface L3-1 sends 660 the maximum congestion level of N    and K in order to report the congestion level to the layer-3. In    this manner, MTP2/NNI-SAAL (layer-2) line congestion is simulated    when the interface between MTP3 (layer-3) and layer-2 is overloaded.    As a result, layer-2 line congestion indications has been aggregated    with the simulated congestion for the interface overload to make a    consistent view for layer-3, wherein layer-2 line congestion    indications indicate congestion between layer-2 instances of the    first and second network nodes 110, 120, respectively. For each    link, the interface (between layer-3 and layer-2) may separately    maintain the level of congestion that was indicated by layer-2 and    the level of congestion based on the amount of not acknowledged    messages towards layer-2. These two levels, i.e. N and K, may be    tied in the interface in such a way that maximum of these two levels    may be indicated to the layer-3. Optionally, it may not be necessary    to send the maximum congestion level of N and K if there is no    changed as compared to a previous report of the congestion level.    Advantageously, sequence problems in case of congestion between    layer-2 instances in the first and second network nodes 110, 120,    respectively and in case of congestion between the layer-2 and the    layer-3 in the first network node may be avoided.-   670 The layer-2 L1-1 send a data acknowledgement message to the    layer-3 L2-1 via the interface L3-1.-   680 The interface L3-1 decrements the counter K due to the data    acknowledgement message.-   690 The interface L3-1 sends the maximum level of N and K.

FIG. 7 shows a second exemplifying, schematic combined signalling andflow chart of an embodiment of the method in the first network node 110for managing congestion of at least one link in a SS7 network protocolstack. Said at least one link interconnects the first network node 110with a second network node 120. The method provides flow control fromM3UA to SCTP under SCTP overload. The SS7 network protocol stackcomprises a layer-2, denoted L1-1, and a layer-3, denoted L2-1, and aninterface, denoted L3-1, therebetween. The first network node 110comprises multiple processing modules. The layer-3 may be M3UA. Thelayer-2 may be SCTP. In this example, the interface (between layer-3 andlayer-2) does not for each link separately maintain the level ofcongestion that was indicated by layer-2 and the level of congestionbased on the amount of not acknowledged messages towards layer-2.Therefore, the interface is only able to report about failure to send(SFN), and thus layer-3 needs to handle buffering. The number ofbuffered messages will be used to determine the number ofnon-acknowledged messages.”

The dotted lines may indicate the steps introduced in this example. Thefollowing steps may be performed. Notably, the order of the steps maydiffer from what is shown below for some embodiments of the method.

-   710, 720 The interface L3-1 passes congestion level N or SFN (Send    Failure Notification) from the layer-2 L1-1 to the layer-3 L2-1.-   730, 740 The interface L3-1 passes data from the layer-3 L2-1 to the    layer-2 L1-1.-   750 The interface detects (or determines) that there are too many    outstanding messages in relation to a certain threshold. Outstanding    messages are messages that have not yet been acknowledged. A level K    is detected. Advantageously, the layer-3 L2-1 may be aware of    overload situation, not only between layer-2 instances in the first    and second network nodes 110, 120, respectively, but also about    overload in the interaction between the layer-2 and the layer-3.-   760 The interface L3-1 sends an internal SFN. When SCTP is    overloaded and the window between M3UA and SCTP becomes closed (see    step 750), subsequent data from M3UA will be rejected by the    interface using SFN (message will be sent internally by the    interface to itself). Again, this is necessary because the interface    L3-1 is not aware of which said at least one link exist(s), whereas    the layer-3 L2-1 is aware which said at least one link exist(s).-   770 The internal congestion level is increased. Right after    reception of a first SFN for association, M3UA will buffer all    subsequent data that should be sent over that particular    association. Depending on the usage of the buffer for messages that    can't be sent due to SCTP overload or interface overload, the M3UA    internal congestion indications (similar to congestion between    layer-2 and layer-3) will be raised (the higher usage of buffer, the    higher level of congestion) to reduce data flow towards overloaded    SCTP.-   780 The congestion level is set to the maximum level of N and K.-   790 The interface L3-1 receives data from the layer-3 L2-1. As soon    as the window towards SCTP becomes opened (credits are received),    M3UA will send all buffered messages (unless SFN received again),    subsequently decreasing congestion level (see step 820) if it was    raised because of buffering. 800 The interface L3-1 sends an    internal SFN.-   810 The layer-3 L2-1 receives data acknowledgement. 820 In response    to the received data acknowledgement in the step 810, the internal    congestion level is decremented, if number of buffered messages is    below a certain threshold.-   830 The congestion level is set to the maximum level of N and K. In    this manner, sequence problems in case of congestion between layer-2    instances in the first and second network nodes 110, 120,    respectively and in case of congestion between the layer-2 and the    layer-3 in the first network node may be avoided. 840 The interface    L3-1 receives data from the layer-3 L2-1

An advantage of the method illustrated in FIG. 7 is that data lossesunder SCTP overload may be decreased. A further advantage is thatcongestion perceived by the second layer remains consistent withexisting second layer implementations.

Even though the invention has been described with reference to specificexemplifying embodiments thereof, many different alterations,modifications and the like will become apparent for those skilled in theart. The described embodiments are therefore not intended to limit thescope of the invention, which is defined by the appended claims.

The invention claimed is:
 1. A method in a first network node formanaging congestion of outgoing data of a link, wherein said linkinterconnects the first network node and a second network node, thefirst network node comprises a first protocol stack comprising a firstlayer, a second layer, and an interface between the first layer and thesecond layer, the second network node comprises a second protocol stackcomprising a first layer, a second layer, and an interface between thefirst layer and the second layer, the method comprising: determining acongestion level between the first and second layers of the firstnetwork node, receiving, from the first layer of the first network node,an existing first layer congestion level indication indicatingcongestion between the first layer of the first network node and thefirst layer of the second network node, generating a simulated firstlayer congestion level indication based on the determined congestionlevel between the first and the second layers of the first network node,and generating a total first layer congestion level indication based onthe simulated first layer congestion level indication and said existingfirst layer congestion level indication.
 2. The method according toclaim 1, wherein the method is performed in the interface of the firstnetwork node and further comprises sending to the second layer of thefirst network node the total first layer congestion level indication. 3.The method according to claim 1, wherein the method is performed in thesecond layer of the first network node and further comprises a step ofmaking the total first layer congestion level indication available tothe second layer.
 4. The method according to claim 1, wherein the stepof generating a total first layer congestion level indication furthercomprises aggregating the simulated first layer congestion levelindication and said any existing first layer congestion level indicationto form the total first layer congestion level indication.
 5. The methodaccording to claim 1, wherein the total first layer congestion levelindication comprises the simulated first layer congestion levelindication, if the simulated first layer congestion level indicationindicates worse congestion than said any existing first layer congestionlevel indication, or said any existing first layer congestion levelindication, if said any existing first layer congestion level indicationindicates worse congestion than the simulated first layer congestionlevel indication.
 6. The method according to claim 1, wherein the firstprotocol stack comprises an SS7 network protocol stack.
 7. The methodaccording to claim 6, wherein the first layer of the first network nodecomprises layer-2 of the SS7 network protocol stack.
 8. The methodaccording to claim 7, wherein the second layer of the first network nodecomprises layer-3 of the SS7 network protocol stack.
 9. The methodaccording to claim 8, wherein the layer-3 is MTP3, when layer-2 is MTP2or NNI-SAAL, or the layer-3 is M3UA, when layer-2is SCTP,
 10. The methodaccording to claim 6, wherein said first layer congestion indicationcomprises layer-2 congestion indication, when the second layer is MTP3or MTP3b, or Send Failure Notification, when the second layer is M3UA.11. The method of claim 1, wherein the first layer congestion levelindicator is not assigned for links that are not overloaded.
 12. Themethod of claim 1, wherein the network node generates a total firstlayer congestion level indication based on the simulated first layercongestion level indication and said any existing first layer congestionlevel indication.
 13. The method of claim 12, wherein the interfacesends the total first layer congestion level indication to the secondlayer based on one or more steps of the method being performed in theinterface.
 14. The method of claim 1, wherein the determined congestionlevel is a simulated congested level, generated by the interface, of notacknowledged messages to the second layer of the first network node. 15.The method of claim 1, wherein the determined congestion level is basedon a number of not-acknowledged messages that exceed a threshold. 16.The method of claim 1, wherein the first layer congestion levelindicator is indicating congestion on a link that is congested betweenthe first network node and the second network node.
 17. An arrangementin a first network node for managing congestion of outgoing data of atleast one link in a telecommunications signalling network protocolstack, comprising a first and a second layer and an interfacetherebetween, wherein each said at least one link interconnects thefirst network node and a second network node, the first network nodecomprises multiple processing modules, wherein at least one of saidmultiple processing modules is configured to determine a congestionlevel between the first and second layers, characterized in that thearrangement further comprises: a receiving unit configured to receive,from the first layer, an existing first layer congestion levelindication indicating congestion between the first layer of the firstnetwork node and the first layer of the second network node, whereinsaid at least one of said multiple processing modules further isconfigured to generate a simulated first layer congestion levelindication based on the determined congestion level between the firstand the second layers, and to generate a total first layer congestionlevel indication based on the simulated first layer congestion levelindication and said existing first layer congestion level indication.18. The arrangement of claim 17, wherein the network node generates atotal first layer congestion level indication based on the simulatedfirst layer congestion level indication and said any existing firstlayer congestion level indication.